Psilocybin Shows Greater Promise Than Cannabis for Treating OCD, Major Review Finds
New Scientific Review Reconsiders Future Treatments for Obsessive-Compulsive Disorder
A review led by scientists at McMaster University suggests that psilocybin may hold greater promise for treating obsessive-compulsive disorder than cannabinoid-based therapies.
Obsessive-compulsive disorder (OCD) is marked by relentless, intrusive thoughts and repetitive behaviours, often demanding lifelong management. Researchers note that the condition stems from a complex interplay of biological mechanisms, with disruptions in serotonin, dopamine and glutamate signaling thought to play a key role.
Standard treatment relies on selective serotonin reuptake inhibitors alongside cognitive behavioural therapy, particularly exposure and response prevention. However, as many as six in ten patients fail to respond adequately, leaving a substantial proportion living with treatment-resistant Obsessive-compulsive disorder (OCD).
Broader discussions on long-term mental health challenges and treatment resistance are frequently explored at Human Health Issues, which examines emerging research into chronic psychological conditions.
Psychedelics Re-Enter psychiatric Research
Over the past decade, psychedelics have re-entered psychiatric research, with growing attention on their potential influence over brain circuits linked to compulsive behaviour, emotional regulation and anxiety.
What the Scientists Examined
In a paper titled "New treatments for OCD? Evidence for cannabinoids and psychedelics", published in the Journal of Psychiatric Research, scientists carried out an extensive scoping review examining the role of psilocybin in obsessive-compulsive disorder, including cases resistant to conventional treatment.
The review drew on both published studies and grey literature, assessing evidence on cannabinoids and several psychedelic substances, including psilocybin, LSD, DMT and methylenedioxyphenethylamine. Much of the data stemmed from case reports and survey-based research, with only a handful of small clinical trials and very limited controlled studies available.
Cannabis Findings Split in OCD Patients
Mixed Outcomes From Medical Cannabis Use
Data collected via the Strainprint smartphone app followed 1,810 cannabis use sessions over a 31-month period among 87 OCD patients prescribed medicinal cannabis for obsessive-compulsive disorder. Users reported fewer intrusive thoughts in nearly 90% of sessions, reduced compulsive behaviours in over 95% and lower anxiety levels in close to 94%. By contrast, symptom worsening was uncommon, occurring in just 3% of intrusion reports, 2.3% of compulsions and 1.9% of anxiety cases.
On average, inhaled cannabis was linked to a 49% drop in intrusive thoughts, a 60% reduction in compulsions and a 52% decrease in anxiety. Higher CBD content and dosage were associated with greater improvements in compulsive behaviour only. While baseline ratings for intrusions and compulsions remained stable over time, anxiety levels prior to use showed a significant downward trend.
An Italian outpatient survey followed 70 individuals diagnosed with primary OCD under DSM-5 criteria, dividing participants into current users, former users and non-users of substances. Around 30% reported using substances to manage obsessive-compulsive symptoms, with cannabis cited by 10%. Only a small fraction of current or past cannabis users said the drug eased their symptoms, while nearly a quarter reported a worsening of OCD, largely linked to heightened anxiety.
Environmental and lifestyle factors affecting mental health outcomes are also discussed on Earth Day Harsh Reality, which connects planetary stressors with human wellbeing.
Psilocybin and Psychedelic Findings Show Stronger Signals
International and Clinical Evidence Emerges
An international retrospective study involving 174 people with OCD from France, Canada, Belgium, United States and Switzerland examined experiences with psychedelic substances. Of all drug categories assessed, classic psychedelics were the only ones consistently associated with meaningful symptom improvement.
Reports on duration were mixed: one-third of participants experienced benefits lasting longer than three months, while another third saw improvements fade within a week following psilocybin or LSD use. Greater symptom relief was linked to more intense and positively perceived psychedelic experiences.
Clinical Psilocybin Evidence Highlights Rapid Effects
Case Reports and Variable-Dose Studies
Clinical evidence on psilocybin has emerged from individual case reports, variable-dose studies and later controlled investigations. One widely cited case involved a 33-year-old man with treatment-resistant OCD who received psilocybin at 0.25 mg per kilogram, equivalent to 19.4 mg. His Yale-Brown Obsessive Compulsive Scale (Y-BOCS) score fell sharply from 23 before dosing to just 2 within 48 hours, before reaching zero at the 12-week follow-up. The patient later reported feeling entirely free of OCD symptoms one year after treatment.
Further findings from a small variable-dose study involving nine individuals with treatment-resistant OCD showed immediate symptom reductions in all participants within 24 hours of at least one dose. Improvements ranged from 23 to 100%, with nearly 90% maintaining a minimum 25% reduction at 24 hours, and two-third sustaining a reduction of at least 50%. No clear relationship was found between dose size and compulsive symptom scores.
Controlled Psilocybin Trial Results
In a controlled within-subjects study, 18 adults with moderate to severe OCD received 10 mg of synthetic psilocybin and a 1 mg active control dose four weeks apart. Symptom scores at one, two and four weeks after the 10 mg dose were significantly improved compared with baseline, with the strongest effect observed after one week.
Findings from LSD-assisted psychotherapy involved two patients with severe, treatment-resistant OCD who received between one and five doses of LSD at levels of 100 to 200 micrograms. One individual entered remission, while the second experienced no improvement.
Clinical Limitations and the Path Forward
The current body of psychedelic research remains limited, relying heavily on small-scale studies and individual case reports, which restrict firm clinical conclusions. To date, there is little evidence to support cannabinoids as viable treatments for OCD, while psilocybin appears to offer more promise for those unresponsive to conventional therapies.
Positive psilocybin signals have already been reported in PTSD, anxiety and depression disorders that share features such as recurring intrusive thoughts. The inclusion of OCD strengthens the case for further investigation through larger randomized controlled trials, robust comparison groups and extended follow-up to determine lasting clinical benefit.
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